1. Field of the Invention
The present invention relates to an image pickup, and more particularly to an image pickup for use in the detection of the driving status of a driver, etc.
2. Discussion of the Background
In recent years, detecting and monitoring the driving status of a driver all the time has been studied related to the drive assist system. In general, a method of taking a face image of a driver by an image pickup camera built in a rear view mirror (hereinafter referred to as a rear view mirror built-in image pickup) is used to detect the status of the driver. Securely taking face images of a driver in a wide range of illuminance from day to night is necessary.
A rear view mirror built-in image pickup adopting a near infrared pulse light projection method is already present to securely take face images of a driver from a low illuminance during night to a high illuminance during daytime. In this rear view mirror built-in image pickup, a light emission unit in which LEDs emitting light having a wavelength of 850 nm are arranged, an image pickup unit of a charge-coupled camera (CCD), etc are built-in a rear view mirror. The rear view mirror built-in image pickup irradiates an object (driver) with beams of near infrared having a wavelength of 850 nm in a pulse manner during which the shutter of the CCD camera is open to receive a reflection light image. When taking an image of a driver, a near infrared bandpass filter mirror which transmits beams of near infrared and reflects optical light required for the driver is used to receive a reflection light image with the CCD camera formed by irradiating the driver with the beams of near infrared without a loss while not hindering the function of the rear view mirror. In this rear view mirror built-in image pickup, images of a driver are securely obtained by using near infrared.
The object of detecting and monitoring the status of a driver during driving is to detect and monitor deterioration of consciousness due to dozing off, inattentive driving, etc. The rear view mirror built-in image pickup described above shoots a face image of a driver, takes out (detects) the face area and eye area from the face image, and measures blinks and the direction of the line of sight. The rear view mirror built-in image pickup detects the degree of deterioration of consciousness from the change in the time of shutting eyes of blinking and inattentive view from the direction of the face and/or the eyeball.
As described above, taking out the face area and the eye area from the face image of a driver taken by an image pickup is necessary to detect the driving status of the driver. Thus, placing the position of those areas at a high speed with high precision is demanded. For example, precision is required such that when a dummy (mannequin) sits at wheel, the dummy's face is not detected as the face of man. The rear view mirror built-in image pickup can securely shoot face images of a driver in the environment in which the illuminance changes from day to night. However, since the rear view mirror built-in image pickup employs a method of using only near infrared light having a single wavelength of 850 nm, placing the position of the face of a driver is limiting with regard to high precision.
In addition, another device, i.e., a near infrared multi-band image pickup, exists and uses near infrared light having a wavelength of 870 nm and near infrared having a wavelength of 970 nm. The near infrared multi-band image pickup irradiates the driver with near infrared having a wavelength of 870 nm and near infrared having a wavelength of 970 nm sequentially to obtain two images of 870 nm and 970 nm by a CCD camera. The image pickup detects the skin and hair portions by calculating the difference between the luminance values of the two irradiation images and discriminates the two portions from the symbol of the difference. The optical light is cut by an optical filter so that a secure image can be obtained.
The near infrared multi-band image pickup makes it possible to place the face of man with high accuracy but since the infrared having a wavelength of 870 nm and the infrared having a wavelength of 970 nm are emitted sequentially, images should be obtained by sequential lighting in a synchronized manner, which causes problems with regard to complexity and real time property.